1. Field of the Invention
This invention pertains to plastic lumber pallets and more particularly to a method and device for joining of plastic lumber to form pallets.
2. Background of the Invention
As the recycling of plastic continues in the United States, there is a great need for the increase in the utilization of the recycled product. Some of the plastic being recycled is ground up and extruded into a product known as plastic lumber. Plastic lumber is similar in shape and texture to its wood counterpart. Recycled plastic lumber offers many of the same features as wood.
An industry utilizing large amounts of both hardwood and softwood is the pallet industry. The pallet industry used 4.5 billion feet of hardwood alone in 1995, which was 37% of the total United States production. The federal government is becoming increasingly concerned about the environmental impact this continued consumption of lumber has on the environment. As the price of wood lumber continues to rise, many segments of this industry are looking for an alternative to wood. A good alternative is plastic lumber. Plastic lumber is made out of post-consumer plastic and can be used in most of the same applications wood lumber is used. One of these uses is in the construction of pallets. The pallet industry has been introducing plastic pallets for some time, but these pallets are made from mainly virgin plastic. Most plastic pallets are made using plastic injection molding, which is a very expensive process. Alternatively, the pieces of the pallet are fastened using metallic screws or bolts which present stress points for fracture and failure and separation problems on recycle. A need exists for an inexpensive and reliable method of joining plastic lumber to form durable plastic lumber pallets. A need exists for a device for quickly aligning and joining plastic lumber into an integral structural unit.
Therefore it is an object of the present invention to produce pallets out of recycled plastic lumber.
Another object of the present invention is to produce strong and reliable joints for plastic lumber pallet structures.
Yet another object of the present invention is to provide a device for joining plastic lumber to form pallets.
Still another object of the present invention is to provide a device that produces plastic lumber pallets of various size.
Another object of the present invention is to provide a support structure for plastic lumber joining.
Yet another object of the present invention is to provide a machine for quickly and accurately aligning plastic lumber for fabrication into a plastic lumber pallet.
Another object of the present invention is to provide a reliable heating source for joining plastic lumber.
Yet another object of the present invention is to provide a recyclable pallet.
Another object of the present invention is to provide a pallet joint of sufficient strength such that the pallet lumber fails prior to joint failure.
Another object of the present invention is to provide a pallet support and fabrication machine that is inexpensive to construct.
Another object of the present invention is to provide a pallet assembly machine that accommodates a wide range of lumber sizes.
Another object of the present invention is to provide a pallet assembly machine that is capable of manufacturing a wide variety of pallet sizes.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail and illustrated in the accompanying drawings. It is contemplated that variations in procedures, structural features and arrangement of parts may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.
The present invention features a machine for forming plastic lumber pallets from plastic runners and plastic cross members. It comprises 1) a cross-member support for supporting one of the pallet cross members, 2) a runner support member for maintaining at least one of the runners in essentially transverse relation with the cross member, and 3) a hot plate positioned between the cross member and one of the runners and heating and melting simultaneously a portion of the top of said cross member and a portion of the bottom of said runner. In addition, the runner support member is formed so as to maintain at least two of the runners in spaced apart relation with respect to each other. A pneumatic vertical movement unit moves the runner support members in an up and down direction. A transverse movement unit moves the hot plate in essentially a transverse direction with respect to the cross-member support. A parallel movement unit moves the hot plate in a direction essentially parallel to that is along the cross-member support. Finally, a vertical movement unit moves the hot plate in an up and down (vertical) direction. Such movement allows the hot plate to be inserted between the runner and cross member and withdrawn when a portion of the runner and cross-member surfaces have been heated to a molten state.
A pressure application member applies pressure to a layered assembly of the hot plate positioned between the cross member and one of the runners during the hot plate heating process in which the hot plate melts simultaneously a portion of the top of the cross member and a portion of the bottom of the runner. The pressure application member also applies pressure to an assembly of a molten portion of the top of the cross member in contact with a molten portion of the bottom of the runner to form the weld or bond between the cross member and the runner. A vertical movement unit is used to move pressure application member in an up an down direction so as to apply pressure to the heating and welding assemblies.
A base such as an assembler table is used to mount the cross-member support, the runner support members, the hot plate and the pressure application member. The pallet assembler table comprises four legs, two ends, and two sides jointed with fasteners such as nuts or bolts for a modular construction or by welding for a more permanent structure, the latter being especially suited for large production runs of pallets of the same size. The machine of the current invention is especially effective for make plastic lumber pallets from solid plastic lumber, especially lumber made from recycled plastics.
The current invention also features a process for welding a plastic lumber runner to a plastic lumber cross-member. Such welds are used to forming the plastic lumber pallet. The process consists of the steps of 1) loading a plastic lumber runner on a runner support member; 2) placing a plastic lumber cross-member on a cross-member support. 3) separating the runner from the cross-member to produce a gap between the runner and cross member, 4) inserting a hot plate in the gap between the runner and the cross member, 5) contacting the runner with a first side of the hot plate and simultaneously contacting the cross member with a second, opposite side of the hot plate, 6) heating the hot plate to a temperature sufficient to form a molten portion of at least one of either the cross member and said runner, 7) separating the runner from the hot plate to form a space between the hot plate and the runner, 8) separating the hot plate from the cross-member, 9) withdrawing the hot plate, and 10) contacting the cross member with the runner in the region of the molten portion to form a weld between the cross member and the runner. The process is further aided by applying a force to the runner, the hot plate, and the cross-member during the heating step and applying a force to the runner and the cross-member during the contacting step of the cross member and the runner to form a weld between the runner and the cross-member.